A 22.5MHz 21.5dBm-IIP3 4th-Order FLFB analog filter

Abstract

A 4th-order single-loop Follow-the-Leader-Feedback (FLFB) low-pass filter is hereby presented. The outstanding FLFB noise behavior has been exploited to release a specific power budget for linearity performance enhancement. Moreover, two pairs of complex poles are synthesized by using a single compact Active-RC cell, avoiding cascade of two or more stages (typically needed for high order filters), and relaxing this way noise power constraints. A prototype of the filter has been integrated in CMOS 0.18μm technological node, having 22.5MHz -3dB low-pass frequency. 21.5dBm in-band IIP3 and 76μVRMS input referred in-band integrated noise have been achieved. The SNR for a -40dB-THD is 69dB. The power consumption is 7mA. The efficiency of the hereby proposed technique is demonstrated by the very high Figure-of-Merit (160J-1) achieved by the FLFB filter comparing with the Active-RC filters state-of-the-art.